# std::binary_negate

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< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class Predicate > struct binary_negate : public std::binary_function< Predicate::first_argument_type, Predicate::second_argument_type, bool >; |  | (until C++11)
template< class Predicate > struct binary_negate; |  | (since C++11) (deprecated in C++17) (removed in C++20)

`std::binary_negate` is a wrapper function object returning the complement of the binary predicate it holds.

The binary predicate type must define two member types, `first_argument_type` and `second_argument_type`, that are convertible to the predicate's parameter types. The function objects obtained from std::owner_less, std::ref, std::cref, std::plus, std::minus, std::multiplies, std::divides, std::modulus, std::equal_to, std::not_equal_to, std::greater, std::less, std::greater_equal, std::less_equal, std::logical_not, std::logical_or, std::bit_and, std::bit_or, std::bit_xor, std::mem_fn, std::map::value_comp, std::multimap::value_comp, std::function, or from a call to std::not2 have these types defined, as are function objects derived from the deprecated std::binary_function.

`std::binary_negate` objects are easily constructed with helper function std::not2.

### Member types

Type | Definition
`first_argument_type` | Predicate::first_argument_type
`second_argument_type` | Predicate::second_argument_type
`result_type` | bool

### Member functions

(constructor) | constructs a new binary_negate object with the supplied predicate (public member function)
operator() | returns the logical complement of the result of a call to the stored predicate (public member function)

## std::binary_negate::binary_negate

explicit binary_negate( Predicate const& pred ); |  | (until C++14)
constexpr explicit binary_negate( Predicate const& pred ); |  | (since C++14)

Constructs a `std::binary_negate` function object with the stored predicate pred.

### Parameters

pred | - | predicate function object

## std::binary_negate::operator()

bool operator()( first_argument_type const& x, second_argument_type const& y ) const; |  | (until C++14)
constexpr bool operator()( first_argument_type const& x, second_argument_type const& y ) const; |  | (since C++14)

Returns the logical complement of the result of calling pred(x, y).

### Parameters

x | - | first argument to pass through to predicate
y | - | second argument to pass through to predicate

### Return value

The logical complement of the result of calling pred(x, y).

### Example

Run this code

    #include <algorithm>
    #include <cstddef>
    #include <functional>
    #include <iostream>
    #include <vector>

    struct same : std::binary_function<int, int, bool>
    {
        bool operator()(int a, int b) const { return a == b; }
    };

    int main()
    {
        std::vector<int> v1;
        for (int i = 0; i < 7; ++i)
            v1.push_back(i);

        std::vector<int> v2(v1.size());
        std::reverse_copy(v1.begin(), v1.end(), v2.begin());

        std::vector<bool> v3(v1.size());

        std::binary_negate<same> not_same((same()));

        // C++11 solution:
        // std::function<bool (int, int)> not_same =
        //     [](int x, int y) -> bool { return !same()(x, y); };

        std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(), not_same);

        std::cout.setf(std::ios_base::boolalpha);
        for (std::size_t i = 0; i != v1.size(); ++i)
            std::cout << v1[i] << " != " << v2[i] << " : " << v3[i] << '\n';
    }

Output:

    0 != 6 : true
    1 != 5 : true
    2 != 4 : true
    3 != 3 : false
    4 != 2 : true
    5 != 1 : true
    6 != 0 : true

### See also

binary_function (deprecated in C++11)(removed in C++17) | adaptor-compatible binary function base class (class template)
function (C++11) | copyable wrapper of any copy constructible callable object (class template)
move_only_function (C++23) | move-only wrapper of any callable object that supports qualifiers in a given call signature (class template)
not2 (deprecated in C++17)(removed in C++20) | constructs custom std::binary_negate object (function template)
ptr_fun (deprecated in C++11)(removed in C++17) | creates an adaptor-compatible function object wrapper from a pointer to function (function template)
unary_negate (deprecated in C++17)(removed in C++20) | wrapper function object returning the complement of the unary predicate it holds (class template)

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